What is Cross Site Scripting? Hackers are constantly experimenting with a wide repertoire of hacking techniques to compromise websites and web applications and make off with a treasure trove of sensitive data including credit card numbers, social security numbers and even medical records. Cross Site Scripting (also known as XSS or CSS) is generally believed to be one of the most common application layer hacking techniques. In the pie-chart below, created by the Web Hacking Incident Database for 2011 (WHID) clearly shows that whilst many different attack methods exist, SQL injection and XSS are the most popular. To add to this, many other attack methods, such as Information Disclosures, Content Spoofing and Stolen Credentials could all be side-effects of an XSS attack.